* chess-input.el (chess-input): New custom group.
(chess-input-notation-type): Put into `chess-input' group.
(chess-input-test-move): Use `chess-ply-keyword' to check for
castling plies instead of doing a string-match on the algebraic
notation string.
* chess-images.el (chess-images-determine-size): Don't use
`x-display-pixel-height' and `x-display-pixel-width' directly.
* chess-display.el (chess-display-draw-square): Make third argument
PIECE optional.